Surface and ground-water origins and interactions and vegetation distributions in riverine and reservoir-fringe systems: A case study in support of reservoir management efforts.

摘要

This dissertation explores surface and ground-water origins and interaction and associated vegetation in riverine and reservoir-fringe systems. The overall objective of this effort is to develop concepts and tools for the planning, implementation, and monitoring stages of river and reservoir management efforts. This study was conducted where Little Stony Creek flows into East Park Reservoir on the east front of the Coast Range, northern California.; Turnover in the local ground-water flow system is rapid indicating that local shallow ground water is dependent upon recent recharge. Little Stony Creek is the more prominent source of local shallow ground water in the wet season, while Franciscan Complex ground water is the more prominent source of local shallow ground water in the dry season.; The flow paths of local shallow ground water are controlled by stream discharge, regional ground-water discharge, and reservoir stage. A ground-water backwater effect caused by the imposed reservoir head extends up valley and supports longer-lived stream discharge and shallower ground water on the delta. During the wet season, changes in stream stage are propagated rapidly across the local ground-water flow system but are slightly attenuated by distance from the channel. During the dry season, stream stage and head on the upper and lower reaches decline steadily and show diurnal fluctuations consistent with evapotranspiration and show abrupt variations likely due to ground-water pumping and rare summer storm events. The effects of changes in stream stage and ground-water pumping are strongly attenuated by the ground-water backwater effect on the delta.; A linked ground-water and vegetation model is developed and used to simulate shallow ground water and vegetation under varying reservoir operations. A numerical ground-water model is constructed, calibrated, and validated and coupled to a vegetation model based on an application of Bayes' Theorem. Four scenarios are simulated: Existing Condition, Existing Condition with Late Drawdown, Full Drawdown, and Full Pool. Compared to the Existing Condition scenario, modeled vegetation distributions do not change under the Existing Condition with Late Drawdown scenario, a xeric herbaceous community type is greatly expanded under the Full Drawdown scenario, and mesic herbaceous, scrub-shrub, and forested community types are greatly expanded under the Full Pool scenario.